The present disclosure relates to a rolling element bearing assembly, and more particularly, to a retention arrangement of a rolling element bearing assembly within a bore of a housing.
As fuel economy becomes paramount in the transportation industry, efforts have increased to achieve higher vehicle and internal combustion (IC) engine efficiencies. Rolling element bearings are well known and can be arranged within IC engines to reduce the friction of rotating shaft assemblies, such as crankshafts, camshafts, and balance shafts. The implementation of a rolling element bearing within such shaft systems requires a thorough design effort to ensure that function and performance targets are met for the life of the IC engine. Design considerations include material hardness and metallurgical cleanliness, surface finish, tolerances, installation fits, operating clearance, and accessibility of lubrication to critical areas of the bearing. The harsh environment of an IC engine, including vibrational loading and substantial temperature fluctuations, contributes to the challenge of designing a rolling element bearing that meets lifetime requirements.
Lightweighting is another means of increasing the fuel economy of today's vehicles. Significant strides have been made in the material sector to provide steel alternatives, such as plastic and aluminum, which not only offer significant weight savings, but also potential improvements in performance and cost. Aluminum cylinder heads and engine blocks are becoming prevalent in the IC engine industry. Additionally, stress analyses to optimize and manage the shape of components have intensified resulting in thinner cross-sections and reduced overall package sizes. Management of the inherent properties of steel alternatives is especially vital in critical applications such as those found in an IC engine.
Rolling element bearings are typically circular in shape, and generally comprise of rolling elements disposed between inner and outer raceways that are integrated within an inner and outer ring, respectively. Rolling elements can take many forms including spherical balls, cylindrical rollers, needle rollers, or various other configurations such as cone-shaped tapered rollers or barrel-shaped spherical rollers. Cages are often used to contain the rolling elements and guide them throughout the rotating motion of the bearing, but are not a necessity in some configurations. The materials of rolling element bearings have remained relatively consistent, with the exception of plastic cages, as steel remains to be the material of choice for the inner and outer rings.
The application of a rolling element bearing with a steel outer ring to a shaft system within an aluminum cylinder head or engine block of an IC engine offers many design challenges. One of these design challenges is providing axial and rotational retention or containment of the rolling element bearing within a bore of an aluminum housing which is typically required for these shaft systems. Given the fact that the coefficient of thermal expansion (COTE) of aluminum is roughly twice as much as steel and that the typical specified temperature operating range is −40 to 150 degrees Celsius, retention designs must manage the extreme size variation of the aluminum housing bore relative to the outer diameter of the steel outer ring of the rolling element bearing.
With view to the prior art in FIG. 1, a rolling element bearing assembly 100 is shown with a retaining ring 120 partially received by a circumferential groove 170 of an outer ring 180. An inner ring 160 and cage 140 to separate and guide rolling elements (not shown) complete the rolling element bearing assembly 100. The retaining ring 120 is designed to reside partially within the circumferential groove 170 and partially within a circumferential groove within a bore of a housing (not shown). Of design importance is the fact that the retaining ring 120 is rotatable within the circumferential groove 170 of the outer ring 180 during use. For this prior art rolling element bearing assembly 100, in the event of a loss of contact between the bore of the housing and the outer diameter of the outer ring, the retaining ring 120 would provide axial containment, however, rotational containment would not be provided. The lack of rotational containment offered by the prior art fails to address the needs of many IC engine shaft systems, therefore, many times these systems eliminate the use of the retaining ring 120 and incorporate a heightened interference fit between the outer ring 180 and housing bore. However, to facilitate retention of the steel outer ring in an aluminum housing at a peak engine temperature of 150° C., a severe interference fit at room temperature (normal installation temperature) is required in order to compensate for the fact that the aluminum bore diameter increases more than the steel outer ring diameter as temperature increases. Due to its severity, such an interference fit can induce stresses beyond the material limits which can lead to immediate or eventual failure as the interference fit becomes more pronounced at cold temperatures when the aluminum bore contracts more than the steel outer ring. In addition, if the wall thickness of the housing around the circumference of the outer ring is non-uniform, the resultant contact pressure between the housing and outer ring will also be non-uniform. In the case of a heightened press-fit, the high contact pressure points could elastically deform the outer ring of the bearing to a non-circular shape, becoming even more pronounced at cold temperatures, again, as the aluminum housing contracts more than the steel outer ring. Any distortion or deformation of the outer ring could potentially lead to premature failure of the bearing.
Yet another consequence of the required severe interference fit between an aluminum housing and a steel outer ring of a rolling element bearing is the effect on the internal bearing clearance, often termed radial operating clearance. The contact pressure that acts on the outer ring in an interference fit condition causes the inner and outer radial surfaces to become smaller in diameter, resulting in the radial operating clearance of the bearing to become less. In the case of an aluminum housing, the greater contraction of the housing bore relative to the steel outer ring at cold temperatures reduces the radial operating clearance even further. In order to avoid too severe of a reduced radial operating clearance condition at temperatures as low as −40° C., the design radial operating clearance is often increased to account for the described effect of an aluminum housing or any housing that has a higher COTE than steel. However, such an adjustment for the ‘cold radial operating clearance’ has a detrimental effect on the ‘hot radial operating clearance.’ Under hot conditions, the aluminum housing bore expands more than the outer diameter of the outer ring resulting in a significant loss in contact pressure, facilitating a growth in size of the outer ring, and causing the radial operating clearance to increase significantly. Additive to this increased radial operating clearance due to thermal expansion is the previously described adjustment clearance, which yields a final radial operating clearance that can be large enough to cause noise and/or excessive axial movement of the shaft, both of which should be avoided in IC engine applications.
Given the preceding discussion, a solution is needed that provides for axial and rotational retention of a rolling element bearing within a bore of a housing while minimizing any detrimental effect on radial operating clearance.